1. Field of the Invention
This invention is concerned with a nuclear reactor fuel rod comprised of a thin-walled tubular casing enclosing the nuclear fuel charge and closed off at both ends by end caps. The rod is also equipped with a mechanism to hold back and, after a time delay, carry off fission products by means of the combination of a gas-absorbing filter material, and of a hole provided in the adjoining end cap. Such nuclear reactor fuel rods are also called vented fuel rods and are used mainly in gas-cooled nuclear reactors. The fuel elements are assembled from them by attaching the fuel elements at the fuel rod support plate by one of the end caps. On the inside or the outside of this place a system of pipes is connected to the gas discharge holes of the individual fuel-rod end caps. After fuel elements of this type are inserted into a nuclear reactor, the manifolds of each fuel element are connected to the gas discharge system of the nuclear reactor plant, which, however, is not the subject of the present invention and will not be discussed in detail.
The gas-absorbing filter material provided in the individual fuel rods, may consist, for example, of activated carbon. Its purpose is to retain the gaseous fission products for a certain time period during which the principal radioactivity of the products can decay. The fission products escaping via the gas discharge lines are thus released only after a time delay and then only when they have a relatively low level of radioactivity. Customarily, this filter material is placed in the tubular casings following the nuclear fuel charge. This solution, however, presents the disadvantage that the space between the tubular casing and the charge of filter material charge cannot in practice be made sufficiently small so that the bypass flow of the gaseous fission products, formed by this design, is negligibly small. Furthermore, by this type of design, the contact between the filter material and the fission products which are to be absorbed does not reach its optimum value.